μLED Tunnel Junction Activation for Low Forward Voltage
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Solution Overview
Problem
Current III-nitride light emitting diodes (LEDs) face challenges with high operating voltages and inefficient current spreading due to difficulties in forming low resistance tunnel junctions, particularly with p-type gallium nitride (p-GaN), which limits their performance and commercialization, especially in micro-size LEDs (μLEDs) for next-generation display applications.
Innovation Solution
The method involves fabricating μLEDs with an epitaxial tunnel junction using MOCVD, incorporating InxAlyGazN insertion layers and n+GaN layers, which reduces the bandgap and enhances tunnel probability, along with access points to activate the p-type layer, resulting in a stable and uniform low forward voltage of 3.08 to 3.3 V at 20 A/cm2, improving current spreading and output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional p-contacts and TCO materials are used for current spreading, then the device structure is simple, but the operating voltage increases significantly and current spreading efficiency decreases
Solution Approach 1:
An n-type tunnel junction layer is introduced as an intermediary between the p-GaN active region and the n-type contact. This tunnel junction enables efficient current spreading through quantum tunneling while maintaining low resistance, thereby reducing operating voltage without complicating the overall device structure
Solution Approach 2:
The tunnel junction layer is highly doped (n+) to change the electrical parameters of the interface, creating a narrow depletion region that facilitates electron tunneling. This parameter change enables low resistance current spreading and reduces the voltage drop across the contact interface
2Reliability
If bandgap engineering with AlN interlayers or InGaN interlayers is used to reduce tunneling barrier, then tunneling probability increases, but voltage loss or resistance increase occurs
Solution Approach 1:
Instead of changing the bandgap through material composition (AlN or InGaN interlayers), the invention changes the doping parameter to create a highly doped n+ tunnel junction layer. This approach reduces the depletion region width and tunneling barrier through high carrier concentration, achieving high tunneling probability without the energy losses associated with bandgap engineering
Solution Approach 2:
The invention uses a simple highly doped GaN layer rather than complex heterostructure interlayers, effectively replacing expensive and lossy bandgap engineering materials with a more efficient doping-based solution
3Ease of manufacture
If Mg doped p-GaN is grown by MOCVD, then the fabrication process is simplified, but hydrogen compensation reduces electrical conductivity
Solution Approach 1:
The n-type tunnel junction layer serves as a mediator that compensates for the low conductivity of Mg-doped p-GaN. By providing a highly conductive n+ path, it bypasses the hydrogen compensation issue in the p-GaN layer while maintaining overall device electrical performance
Solution Approach 2:
The contact structure is segmented into multiple functional layers: the Mg-doped p-GaN layer provides hole injection, while the separate n-type tunnel junction layer provides low resistance electron transport. This segmentation allows each layer to optimize its specific function without compromising the other
4Reliability
If two separate deposition techniques (MOCVD and MBE) are used to fabricate tunnel junction μLEDs, then the p-type region remains electrically conductive, but fabrication complexity and cost increase
Solution Approach 1:
The invention merges the fabrication process by growing both the p-GaN active region and the n-type tunnel junction layer using a single MOCVD technique. This eliminates the need for separate MBE deposition, reducing fabrication complexity and cost while maintaining the electrical conductivity of the p-type region through proper process parameter control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables μLEDs with reduced forward voltage, improved current spreading, and higher output power, facilitating the integration of multiple emission colors like blue, green, and red, and simplifying the fabrication process, making them suitable for various applications including micro-displays.
Implementation Method 1
A tunnel junction is a diode comprised of a very highly doped (n+/p+) interface that allows for electrons to tunnel between the valence band and conduction band
Implementation Method 2
an epitaxial tunnel junction comprised of p+GaN, InxAlyGazN insertion layers, and n+GaN layers grown using MOCVD
Data Source
AI summary
A method to fabricate micro-size III-nitride light emitting diodes (μLEDs) with an epitaxial tunnel junction comprised of a p+GaN layer, an InxAlyGazN insertion layer, and an n+GaN layer, grown using metalorganic chemical vapor deposition (MOCVD), wherein the μLEDs have a low forward the GaN layers, which reduces a depletion width of the tunnel junction and increases the tunneling probability. The μLEDs are fabricated with dimensions that vary from 25 to 10,000 μm2. It was found that the InxAlyGazN insertion layer can reduce the forward voltage at 20 A/cm2 by at least 0.6 V. The tunnel junction μLEDs with an n-type and p-type InxAlyGazN insertion layer had a low forward voltage at 20 A/cm2 that was very stable. At dimensions smaller than 1600 μm2, the low forward voltage is less than 3.2 V.